Birds BMW M140i (2021) review: the afterlife | CAR Magazine
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Birds BMW M140i (2021) review: the afterlife

Published: 25 June 2021 Updated: 25 June 2021
Birds BMW M140i (2021) review: the afterlife
  • At a glance
  • 5 out of 5
  • 5 out of 5
  • 5 out of 5
  • 5 out of 5
  • 4 out of 5

By James Taylor

Former features editor for CAR, occasional racer

By James Taylor

Former features editor for CAR, occasional racer

► Sensitively modded 1-series tested
► Suspension and diff upgrades for
► Full conversion costs £4817+VAT

Aside from the little ‘fitted with a Quaife differential’ sticker in the rear window, this red BMW M140i could easily be mistaken for a regular, previous-generation 1-series. But there’s more to this car than meets the eye.

This car has been carefully and sensitively altered by Bucks-based BMW tuning specialists Birds. New springs, dampers, altered track width, a potent engine management upgrade, serious front brakes and different tyres as well as the aforementioned ATB limited-slip diff make this a thoroughly overhauled car. 

It’s a rolling catalogue for Birds’ range of tuning parts, available separately or together in packages, and the sum total is a car that feels more rounded and exploitable than the regular M140i on British roads. This is a great driver’s car. 

What is Birds and what does it do?

Birds as a company has been around the motor industry since the 1930s and started getting involved with BMW in the early ’70s, originally as a dealer. In the late ’80s technical director Kevin Bird developed a tuning arm of the business, which today focuses on suspension tuning and limited-slip differentials to open up the ride and handling envelope of BMWs past and present. ‘That’s what makes us unique,’ Bird says. ‘there are many companies which can offer power upgrades, but we focus on making changes that you can enjoy at any speed, and often enable you to get more out of the car overall.’

Birds offers ECU upgrades of its own too (in this car’s case, boosting power to 424bhp) but the handling tweaks are the most intriguing bits of this package.

What’s actually different on this particular car?

Birds B-sports kit includes new springs, dampers and a wider front track. The latter alters the front scrub radius, removing some of the factory-spec autobahn ‘sneeze factor,’ and making the M140i much more alert to the first degrees of steering angle. 

The set-up has been developed on road and track by former professional racing driver and Daytona 24hr winner James Weaver, who Kevin Bird first met when Weaver was campaigning 6-series BMWs in European Touring Car racing.

birds m140i cornering

This isn’t some solid-sprung trackday special, however: the aim is to be an enjoyable set-up for everyday road use, first and foremost. To that end, ride comfort is more than smooth enough, both at low speeds over speedbumps and attacking a bumpy road at speed.

The M140i’s original run-flat tyres have been switched to Goodyear Eagle F1’s, chosen at Weaver’s suggestion because they work well in all temperatures all year round down to around 4decC (stickier tyres tend to stop being useful below around 7 degrees).

An automatic torque-biasing Quaife limited-slip diff gives the M140i greater traction and a more precise feel when putting its power down. (Almost all M140is from the factory were fitted with open differentials.) The M140i no longer spins its inside rear wheel if the driver gets heavy-handed, and, should they wish, power oversteer is easier and more controllable too. 

Birds offers a variety of ECU upgrades, including a 375bhp option but this car has the top 424bhp option (up from around 335bhp in the standard car). Torque increases to 419lb ft @ 3200rpm (from 369lb ft @ 1,500-4,500rpm).

birds m140i engine

For manual cars, Birds offers a quick-shift kit and also alters the spring on the clutch pedal, making its action feel weightier and more precise.

An upgrade to beefy 365x32mm Alcon brakes up front.

And how does it all feel on the road?

In the interests of an apples-to-apples comparison, I borrowed CAR art editor Mal’s standard M140i for a back-to-back drive (a careful one, Mal, honest). 

First thing you notice is the altered scrub radius. The steering responds much more instantly to inputs either side of the straight-ahead, although the power steering is still light and there’s still not a great deal of feel through the standard rack. (Birds has looked at fitting its own steering rack but it simply wouldn’t be cost-effective.)

Over bumps at urban speeds, the Birds car feels taut but not uncomfortable; it’s smoother riding than our long-term Toyota GR Yaris, for example. In fact, there’s quite a bit of body movement, particularly in terms of squat at the rear. It’s not as tightly contained as a lot of modern performance cars but that’s emphatically not a bad thing. It underlines that this is a car that’s been designed to be enjoyed on everyday roads, day-in, day-out.

birds m140i side pan

That also translates into a ride that’s very comfortable at a cruise on the motorway too. There’s perhaps a little bit more road noise transmitted through the suspension components than on the factory car, but only by a very small amount.

Get it onto an undulating B-road and the Birds set-up all makes sense; really good sense. Think of it less as a sports pack and more of a ‘Brit pack,’ well-suited to this country’s roads. Compared with the factory-spec M140i, the Birds car is a fraction more composed in every respect: more controlled into compressions and over crests; the steering less prone to wandering over the crown of the world; ride a tad smoother (though the non-run-flat Goodyears help in that regard too).

Settled into a corner, the Birds car’s resting bias is towards subtle, and safe, oversteer – not just under power but in steady-state cornering too, with perhaps a touch of roll-steer from the suspension setup. It doesn’t feel nervous or snappy. And from the moment you pick up the power (nice and early thanks to the ECU’s progressive torque delivery), the Quaife limited-slip diff can be used to hook up nicely and drive the car forwards (or if you wish, very slightly sideways) out of the corner. 

It flows well, and it’s an easy car to get in a rhythm with. 

Parked next to the factory-spec car, there’s something very subtly different about the Birds car’s stance, but it’s no slammed, big-camber affair. In fact, this particular car rides with a very small amount of rake, sitting 5mm lower at the front and up 5mm at the rear.

birds m140 rear cornering

With the engine management upgrade to 424bhp, this is a rapid car. With no outward clues as to its potency and its 18-inch standard wheels looking relatively small for a modern car, it’s a real sleeper and no mistake. 

In this manual car (a rarer find than an auto; there are around 1100 or so manual M140is on the road in the UK), the short-throw gearchange is more positive than the standard slack, elastic-feeling BMW shift pattern. The weightier clutch action feels more positive and progressive, too. 

As does the engine. Although it’s potent enough to rock the car across its axis when blipping the throttle at a standstill, torque delivery is deliberately limited in the first three gears. That gives it a nicely progressive, almost naturally aspirated feel. You can feed the power in precisely, and it really gets going towards the top of the rev range, for a nice crescendo feel. 

That said, the standard M140i engine feels more than quick enough to me, and it feels like there’s more to be gained and enjoyed from the suspension and the diff than by upping the power.

How much does all this cost?

For the Full English (suspension, front track, diff, 424bhp engine management livener, short-shift kit and more), you’ll need £4818 plus VAT.

For an auto car, without the short shift and clutch mod it’s £4264 plus VAT.

Alternatively, you can just choose the suspension and diff as a Dynamics Package at £2945 + VAT, or pick ‘n’ mix individual components.

What next?

Since the BMW 1-series went front-wheel-drive (and its quickest variants went four-wheel-drive) a couple of years ago, the older versions have become something of a lost treasure. A new hot hatch with a straight-six engine driving the rear wheels won’t be along any time soon. 

There will be a rear-wheel-drive 2-series Coupe (and you can read Georg Kacher’s prototype drive here) but there’s no longer a rear-wheel-drive 1-series. The new, transverse-engined M135i is all-wheel-drive.

‘In the future, I think we have to look after these cars because they’re not being replaced,’ Kevin Bird says. ‘I suspect we will continue to focus on analogue driving machines just as long as we can.’


You can still just about buy a brand-new M140i as dealers work their way through the last of the European production run, while second-hand cars are available from around £17,000 (and older M135i models from around £10k). If you’re lucky enough to have one in your possession, the Birds upgrades are a sympathetic and effective way to broaden its palette of dynamic colours. 

Although the ECU upgrade gives this car enormous performance, the suspension mods make more sense than the power upgrade, giving the 1-series a sweetly judged blend of backroads agility and everyday usability. 

birds m140i rear cornering


Price when new: £5,781
On sale in the UK: Now
Engine: 2998cc 24v turbocharged straight-six, 424bhp @ 6600rpm, 419lb ft @ 3200rpm
Transmission: Six-speed manual with quickshift kit, limited-slip differential, rear-wheel drive
Performance: 4.2sec 0-62mph (est), 155mph
Weight / material: 1450kg
Dimensions (length/width/height in mm): 4324/1765/1411mm

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  • Birds BMW M140i (2021) review: the afterlife
  • Birds BMW M140i (2021) review: the afterlife
  • Birds BMW M140i (2021) review: the afterlife
  • Birds BMW M140i (2021) review: the afterlife
  • Birds BMW M140i (2021) review: the afterlife
  • Birds BMW M140i (2021) review: the afterlife
  • Birds BMW M140i (2021) review: the afterlife
  • Birds BMW M140i (2021) review: the afterlife
  • Birds BMW M140i (2021) review: the afterlife

By James Taylor

Former features editor for CAR, occasional racer